Electrical oscillators are used in various types of electronic equipment for instance in equipment where microprocessors and/or communications means are involved.
Especially in communications means the oscillator is a very central device for obtaining timing and modulation/demodulation. In order to obtain modem high speed communication, a stable and precise oscillator is required. Further, since small size and long duration battery operation is typically in demand the oscillator consequently has to be small sized and consume a minimum of electrical power.
An oscillator for the above devices fulfilling the demands is typically implemented by means of a crystal mounted on printed circuit board, connected to an active device, e.g. a CMOS transistor in an integrated circuit providing an oscillator signal to components or subcircuits in the integrated circuit by energizing the crystal to make the crystal generate the oscillator signal. This may provide for an accurate oscillator signal.
Ideally the whole oscillator should be placed in the chip, but this would require too much substrate area on in the integrated circuit. Preferably, the active device is within the integrated circuit where it can be implemented easily along with other active devices in subcircuits using the oscillator signal. Moreover, the least possible number of active devices should be used i.a. in order to minimize power consumption as indicated above.
However, those facts, in combination with design rules and physical limitations impose very strict limitations on a circuit designer in creating the geometrical layout of the electrical connections between the resonator and the active device. Thus it cannot be ensured that the electrical connections are designed to follow a path not subjected to noise induction on the connections. As a matter of fact noise induction is a problem due to often heavy use of digital/logic gates and subcircuits in the integrated circuits, especially for those arranged for communications purposes.
A first known oscillator is implemented by means of a crystal mounted on a printed circuit board, connected to an active device e.g. a CMOS transistor in an integrated circuit providing an oscillator signal to components or subcircuits in the integrated circuit by energizing the crystal to make the crystal generate the oscillator signal. The oscillator signal is provided as the output of an inverter with its input connected to a terminal of the crystal by means of an electrical connection.
However, such an oscillator will be very sensitive to noise induced on the electrical connection. This in turn will ruin extraction of exact timing and oscillation information from the oscillator signal.